I propose to develop a new gene-enzyme system as a probe of eukaryote gene organization. Specifically, my goal is to gain an understanding of the regulation of the expression of the nervous system enzyme acetylcholinesterase in Drosophila melanogaster, via the genetic dissection of its controlling apparatus. Taking advantage of some attractive features of this system, I will study the organization of the acetyl-cholinesterase structural gene. First, mutants will be isolated by: (1) identification of natural variants of acetylcholinesterase; (2) generation of conditional mutants which are sensitive or resistant to anticholinesterases; and (3) production of null-enzyme mutants, which behave as recessive lethals. Mutants which map at the acetylcholinesterase structural gene will be identified. Then, these mutants will be subjected to genetic fine structure analysis to delimit the acetylcholinesterase structural sequence. The acetylcholinesterases produced by the mutant strains will be characterized. Developmental and behavioral effects of these mutants will also be studied. In addition, deletion and complementation analysis of the region surrounding the acetylcholinesterase structural gene will be carried out. Preliminary results are described. The location of this structural gene near the rosy locus and the heat-inducible 87Cl puff will allow synthesis of chromosomes in which elements of these loci can be fused. This fusion will generate some important strains for cloning the acetylcholinesterase gene. In addition, it may place the acetylcholinesterase structural gene under the regulation of a heat inducible control sequence. The experiments outlined in this proposal will provide the genetic background necessary to search for and characterize control mutants at the structural locus and elsewhere in the genome. They will also provide the raw material for the study of the enzymology of Drosophila acetylcholinesterase, and for the study of the developmental and neurophysiological effects of aberrant forms of the enzyme.